1. Field of the Invention
The present invention relates to a bactericide containing ferric ions (Fe.sup.3+) and one or more members of the group consisting of sorbic acid, benzoic acid, and para-hydroxybenzoic acid esters, and to a bactericide containing ferric ions (Fe.sup.3+), L-ascorbic acid, and one or more members of the group consisting of sorbic acid, benzoic acid, and para-hydroxybenzoic acid esters, which can be used in a wide range of applications, from the sterilization of hands and wounds, to the sterilization of furniture, tools, and objects, to the sterilization of fresh foods prior to cooking.
2. Description of the Related Art
Despite the sophisticated roadway system and communication network, huge budgets, numerous CDC (Center for Disease Control) personnel, and state-of-the-art medical treatment available in a developed country like the United States, and even though it has been 16 years since the discovery of Escherichia coli O-157, there are still more than 20,000 new patients each year, and over 200 deaths. In Japan as well, there were numerous mass infections in 1996, and at the present time the situation is still far from static, to the extent that there are researchers who say that this O-157 is a "microbe" that can survive anywhere in the environment and causes infection at a very low bacterium count, and furthermore it is a known fact that there is no way to halt the onslaught of tubercule bacilli or staphylococci with resistance to multiple drugs.
Moreover, in developing countries, oral infectious diseases such as dysentery and cholera are as rampant as ever, and respiratory infectious diseases such as tuberculosis are also widespread. There are currently twenty million patients with tuberculosis in the world, and while most of these are in Africa and other developing countries, there are eight million new cases each year, and the annual number of deaths is said to be in excess of three million. While ignorance about infectious diseases and poor public sanitation cannot be overlooked, these facts are probably also attributable to the fact that people have no antiseptic that allows instantaneous disinfection and is very safe.
Of the sterilization and disinfection methods in daily use today, alcohols, phenols, halogen compounds, quaternary ammonium salts, biguanide-based chemicals, aldehydes, and the like have been put to practical use as chemical methods, aside from such physical methods as heat and radiation. However, there is no product that is satisfactory in all respects, such as a good bactericidal effect, safety, low toxicity, excellent stability and shelf life, and low price. For instance, a biguanide-based chemical sold under the trade name Hibitane is an excellent, best-selling antiseptic, but it is ineffective against spores. Also, resistance has been noted in some bacteria, and this is known to be a cause of hospital acquired infection. There is no need to mention antibiotics, and as for chemical synthetics that are discomforting to microbial cells, resistant strains that render these ineffective always appear as a result of the production of enzymes or the production of substitute enzymes, and these are once again showing up as a threat to humans.
It is already known that certain types of metal ions have a bactericidal action over a specific concentration, and these have been applied in mercury preparations and the like. Mercury, however, is a heavy metal that is completely unnecessary in the body, and furthermore it is extremely toxic, so it has yielded its position as an antiseptic as the various antiseptics mentioned above have been developed, and ever since then antiseptics that make use of metal ions have been virtually ignored. More recently, metal elements have been recognized as essential substances in the body, and their dark image, first as poisons or alchemy and then as environmental pollutants in more recent years, has been swept away, until they are now considered one of the important elements that protect our health, with various minerals and tablets containing these being crowded together with foodstuffs in American supermarkets and the like.
Various metal ions were tested for their bactericidal effect on the major pathogenic bacteria, with the upper limit of the metal ion concentration set at 1000 ppm and the concentration set so as to exhibit the highest efficacy. The test method involved adding a suspension of sample bacteria (1.times.10.sup.9 cells/mL physiological saline) in an amount of 2 wt % to a metal ion solution, allowing 60 minutes for the contact time with the bacteria, sampling 10 .mu.L of the treated liquid, culturing the samples in the optimal environment for each type of bacteria, and observing the viability of the bacteria. As a result, the same efficacy was exhibited, with the exception of spore forming bacteria. For the test, methicillin resistant Staphylococcus aureus (MRSA) was selected from among staphylococci as a typical Gram-positive bacterium, and Escherichia coli O-157 was selected from among Escherichia coli as a typical Gram-negative bacterium. These test results are given in Table 1. As is seen in Table 1, bactericidal action was noted for cupric ions (CU.sup.2+) and ferric ions (Fe.sup.3+). Viability of the bacteria was expressed as ++ when the bacteria proliferated normally with no impediment whatsoever, as + when they were damaged and their proliferation was somewhat inhibited, as .+-. when they were damaged and their proliferation was inhibited, and as - when they did not proliferate and were eradicated.
TABLE 1 Bactericidal action of various metal ions Metal Viability ion Compound name MRSA O-157 Cu.sup.2+ CuSO.sub.4.5H.sub.2 O - - Zn.sup.2+ ZnSO.sub.4.7H.sub.2 O + - Mn.sup.2+ MnSO.sub.4.5H.sub.2 O ++ ++ Co.sup.2+ CoCl.sub.2.2H.sub.2 O ++ ++ Ni.sup.2+ NiSO.sub.4.6H.sub.2 O + + Li.sup.+ Li.sub.2 SO.sub.4.H.sub.2 O ++ ++ Ca.sup.3+ CaCl.sub.2.2H.sub.2 O ++ ++ Mg.sup.2+ MgSO.sub.4.7H.sub.2 O ++ ++ Si.sup.4+ SiO.sub.2 ++ ++ Rb.sup.+ Rb.sub.2 SO.sub.4 ++ ++ Al.sup.3+ Al.sub.2 (SO.sub.4).sub.2.12H.sub.2 O + + Fe.sup.2+ FeCl.sub.2 + + FeCl.sub.2.4H.sub.2 O + + Fe(CH.sub.3 CHOHCOO).sub.2.3H.sub.2 O + + FeC.sub.2 O.sub.4.2H.sub.2 O + + FeSO.sub.4.7H.sub.2 O + + Fe.sup.3+ FeCl.sub.3 - - FeCl.sub.3.6H.sub.2 O - - Fe(NO.sub.3).sub.3.9H.sub.2 O - - Fe.sub.2 (SO.sub.4).sub.3.nH.sub.2 O - - FeC.sub.6 H.sub.5 O.sub.7.nH.sub.2 O - - FePO.sub.4.nH.sub.2 O - -
Next, if we examine the relation between concentration and bacterium contact time for the bactericidal effect of ferric ions (Fe.sup.3+), we see that an effect is gradually exhibited from 400 ppm upward, as shown in Table 2, and at 1000 ppm an effect is exhibited at a bacterium contact time of 5 minutes. The viability of the bacteria was evaluated the same as in Table 1.
TABLE 2 Bactericidal action of ferric ions (Fe.sup.3+) Concentration Contact time Viability as Fe.sup.3+ (ppm) with bacteria MRSA O-157 100 10 seconds ++ ++ 1 minute ++ ++ 5 minutes ++ ++ 200 10 seconds ++ ++ 1 minute ++ ++ 5 minutes ++ ++ 400 10 seconds ++ ++ 1 minute ++ ++ 5 minutes + .+-. 800 10 seconds + + 1 minute + .+-. 5 minutes .+-. - 1000 10 seconds + .+-. 1 minute + .+-. 5 minutes .+-. -
Meanwhile, the bactericidal action of sorbic acid, calcium sorbate, benzoic acid, sodium benzoate, and other such compounds known as food preservatives was examined. The concentration was 1000 ppm, and the contact time with the bacteria was 5 to 120 minutes, after which 10 .mu.L of treated liquid was sampled and cultured in the optimal environment for each type of bacteria, and the viability of the bacteria was observed. As shown in Table 3, the test results for methicillin resistant Staphylococcus aureus (MRSA) and Escherichia coli O-157 indicated no bactericidal action in a short time, and when the contact time was extended to between 30 and 60 minutes, there was finally a bacteriostatic action or bacterial action. Viability of the bacteria was expressed as ++ when the bacteria proliferated normally with no impediment whatsoever, as + when they were damaged and their proliferation was somewhat inhibited, as .+-. when they were damaged and their proliferation was inhibited, as (-) when the coloring of the bacteriostatic action was darker than that of the bactericidal action, and as - when they did not proliferate and were eradicated.
TABLE 3 Bactericidal action of food preservatives Food Contact time Viability preservative with bacteria MRSA O-157 sorbic acid 5 minutes ++ + 15 + + 30 (-) (-) 60 (-) (-) 120 (-) (-) calcium 5 minutes ++ ++ sorbate 15 + + 30 .+-. (-) 60 (-) (-) 120 (-) (-) benzoic acid 5 minutes ++ ++ 15 + + 30 (-) (-) 60 (-) (-) 120 (-) (-) sodium 5 minutes ++ ++ benzoate 15 + + 30 .+-. .+-. 60 (-) (-) 120 (-) (-)
Pathogenic bacteria have long posed a threat to mankind, and it has been a goal in the food industry and the medical profession to develop a bactericide that would have a high degree of practicality which included spores in its scope, that would exhibit a pronounced effect on pathogenic bacteria, that would be safe for humans and the earth, and that would be composed of metal ions having affinity with the body, that is, those which are essential structural components for the body, and compounds that are used in food additives.